From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753711AbaLAQ1p (ORCPT ); Mon, 1 Dec 2014 11:27:45 -0500 Received: from 8bytes.org ([81.169.241.247]:51484 "EHLO theia.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753063AbaLAQ1m (ORCPT ); Mon, 1 Dec 2014 11:27:42 -0500 Date: Mon, 1 Dec 2014 17:27:40 +0100 From: Joerg Roedel To: Jiang Liu Cc: David Woodhouse , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] iommu/vt-d: Fix an off-by-one bug in __domain_mapping() Message-ID: <20141201162740.GK3762@8bytes.org> References: <1416966130-866-1-git-send-email-jiang.liu@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1416966130-866-1-git-send-email-jiang.liu@linux.intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 26, 2014 at 09:42:10AM +0800, Jiang Liu wrote: > There's an off-by-one bug in function __domain_mapping(), which may > trigger the BUG_ON(nr_pages < lvl_pages) when > (nr_pages + 1) & superpage_mask == 0 What is the superpage_mask? > The issue was introduced by commit 9051aa0268dc "intel-iommu: Combine > domain_pfn_mapping() and domain_sg_mapping()", which sets sg_res to > "nr_pages + 1" to avoid some of the 'sg_res==0' code paths. > > It's safe to remove extra "+1" because sg_res is only used to calculate > page size now. >>From your description and the (hard to read) code in __domain_mapping I don't really understand the issue yet. Can you please elaborate on this issue can be triggered? Is the BUG_ON the only issue and, if yes, can that be fixed by just changing the BUG_ON condition? > This issue was introduced in v2.6.31, but intel-iommu.c has > been moved into drivers/iommu in v3.1. So what's the preferred way > to deal with stable kernels between v2.6.31 and v3.1? Just remove the kernel version marker from the stable tag. The stable kernel maintainers for kernels >3.1 will ask you to backport the patch or just backport it by themselfes. Joerg